When to useCallback VS useMemo

In the expansive ecosystem of React, hooks play a pivotal role in crafting functional components and managing their state and side effects. Among these hooks, useCallback and useMemo stand out for their ability to optimize performance, albeit serving distinct purposes.

useCallback

useCallback is a hook designed to memoize functions. This means it caches a function instance between renders, preventing the creation of a new function if the dependencies have not changed. This is particularly beneficial when passing callbacks to optimized child components that rely on reference equality to avoid unnecessary renders.

const memoizedCallback = useCallback(
  () => {
    doSomething(a, b);
  },
  [a, b, // Dependencies
);

useMemo

useMemo is a built-in React hook that accepts 2 arguments; a function compute that computes a result and the dependencies array.

const memoizedData = useMemo(
  () => {
    computeExpensiveValue(a, b)
   },
   [a, b] // Dependencies
);

During initial rendering, useMemo invokes compute, memoizes the calculation result and returns it.

If during the next renderings the dependencies don’t change, then useMemo doesn’t invoke compute but returns the memoized value

Distinguishing Their Use Cases

While both hooks aim at reducing the computational cost, their application scenarios differ. Use useCallback when you need to maintain the same function instance across renders, which is crucial for performance optimization in components that rely on reference equality for prop comparisons. useMemo is your go-to for avoiding expensive recalculations, caching the result of computations instead of function instances.

Performance Considerations

It's important to use these hooks judiciously. Overuse can lead to memory overhead because memoized values and functions must be stored. Assess the complexity of computations and the frequency of re-renders to make an informed decision about employing these hooks for optimization.

In Summary

React's useCallback and useMemo offer powerful means to enhance your application's performance. Choosing between them hinges on whether you're aiming to memoize functions with useCallback or compute values with useMemo. Understanding their distinct roles and applying them wisely can significantly improve your app's efficiency and responsiveness.

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